Method of making a respiration sensor

ABSTRACT

A plurality of flow sensors are fabricated on a single substrate. The substrate is laid out to provide the proper physical relationship of the individual sensors. The resulting multiple sensor structure may be effectively used as a respiration detector by positioning a different sensor element at each of the airflow orifices (i.e., two nostrils and mouth) of a patient. In the preferred embodiment, the sensors are thermoresistive elements, which are screened on the substrate using conductive ink. The change in temperature of the air flow in relation to the ambient at each orifice provides an indication of the flow and may be used to determine the extent of the flow. The substrate is packaged in a single piece adhesive strip which provides ease of proper attachment by the patient.

This application is a continuation of U.S. application Ser. No.08/685,210, filed Jul. 23, 1996, now abandoned, which in turn is acontinuation of U.S. application Ser. No. 08/390,929, filed Feb. 17,1995, now abandoned, which is a continuation of U.S. application Ser.No. 08/201,045, filed Feb. 24, 1994, now abandoned, which is acontinuation of U.S. application Ser. No. 07/934,725, filed Aug. 24,1992, now abandoned, which is a divisional of U.S. application Ser. No.07/665,552, filed Mar. 5, 1991, now U.S. Pat. No. 5,161,541.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to respiration sensortechnology, and more particularly, relates to respiration sensortechnology for detecting abnormal breathing of a patient.

2. Description of the Prior Art

It is known in the art to employ respiration sensors to monitorpatients' susceptible to sleep apnea and other disorders of therespiration system. U.S. Pat. No. 4,878,502 issued to Dietz discusses abreathing sensor employing a tubular passage in which a ball is free tomove to break a beam of light. The ball is moved in response to the flowof air associated with the breathing of the patient. An optoelectricinhalation sensor using thin film deposition is discussed in U.S. Pat.No. 4,745,925 issued to Dietz.

Acoustic sensors for monitoring respiration are mentioned in U.S. Pat.No. 4,602,644 issued to DeBenedetto et al., and in U.S. Pat. No.4,595,016 issued to Fertig et al. U.S. Pat. No. 4,366,821 issued toWittmaier et al. shows a respiration monitoring system which preferablyuses a gas sensor, and U.S. Pat. No. 4,350,166 issued to Mobarry shows avideo monitor. Moisture is sensed using a sodium chloride crystal inU.S. Pat. No. 4,326,404 issued to Mehta.

U.S. Pat. No. 4,306,867 issued to Krasner shows the use of a pressuresensor. An impedance plethysmograph is employed in U.S. Pat. No.4,289,142 issued to Kearns. The use of thermoresistive sensors issuggested in U.S. Pat. No. 3,903,876 issued to Harris, U.S. Pat. No.3,884,219 issued to Richardson. et al., and U.S. Pat. No. 3,999,537issued to Noiles.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages found in the prior artby providing a plurality of sensors fabricated on a single substrate. Itis advantageous to employ multiple sensing elements positioned at thevarious orifices which vent the upper airway of a patient. In the normalcase, the three orifices are the two nostrils and the mouth. Duringsleep, these three orifices are used in various combinations dependingupon individual habits, condition of the respiratory system (e.g. colds,etc.), and type of sleep to monitor the total respiratory effort.

The substrate is packaged within a single adhesive strip, which enablesthe patient to readily apply the sensor to the upper lip. The substrateis not planar placing the individual sensing elements directly into theair stream and out of contact with the skin of the patient. The sensingelements are each inclined from the plane of the substrate away from thepatient.

The sensing elements may be produced using a number of technologies. Inthe preferred embodiment, a conductive ink having a high temperaturecoefficient of resistance and high resistance is applied to thesubstrate using a silk screening process. The individual sensingelements are interconnected in series using a conductive ink having alow resistance, and preferably low temperature coefficient ofresistance. The interconnections are silk screened during a secondprocessing step.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of the present invention and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, in which like reference numerals designate like partsthroughout the figures thereof and wherein:

FIG. 1A is a plan view of a thin film multiple sensor system;

FIG. 1B is a plan view of a conductive ink. multiple sensor system;

FIG. 2 is an electrical schematic diagram of a multiple sensor system;

FIG. 3 is a plan view of a multiple sensor system with electricalconnector;

FIG. 4 is a plan view of a multiple sensor system packaged within anadhesive strip;

FIG. 5 is a partially disassembled view of the multiple sensor package;

FIG. 6 is a side sectioned view of the components of the multiple sensorpackage;

FIG. 7 is a side view of the multiple sensor package;

FIG. 8 is a frontal view of a patient having the multiple sensor packagein place; and,

FIG. 9 is a side view of a patient showing the multiple sensor packagein partially sectioned form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a plan view of a thin film multiple sensor system suitablefor respiration monitoring. This embodiment employs a flexible substrate34 of an insulating material such as a polyimide or polyester upon whichindividual sensing elements. 12, 14, and 16 are deposited using standardthin film deposition techniques. Alternative embodiments use conductiveink, thick film, metal foil or printed circuit board techniques. Thedeposited metalization layer is of a conductor, such as gold, having ahigh temperature coefficient of resistance, and relatively highresistance with respect to the resistance of the interconnectingconductive paths. In order to achieve a high resistance ratio betweenactive elements and conductors, the individual sensing elements 12, 14,and 16 consist of narrow conduction loops coupled in series.

The individual sensing elements 12, 14, and 16 are electrically coupledin series by low resistance conducting paths 22, 24, 26, and 28.Connector pads 18, 19, 20 and 21 provide for electrically coupling themultiple sensor system to apparatus for measuring the resistance changesof the system. Test connector pad 30, along with connector pads 18, 19and 20 permit testing each of the individual sensing elements.

Tabs 36, 38, and 40 are portions of substrate 34 configured to permitease of positioning multiple sensor system 10 above the upper lip andbelow the nasal septum of the nose of a patient. Tab 36 may be madeconcave in order to aid in centering the sensor system under the nose.When substrate 34 is properly positioned, individual sensing elements 12and 14 are located within the air stream to and from the nostrils of thepatient. Similarly, individual sensing element 16 is thus positionedwithin the air stream of the mouth of the patient.

As a patient exhales, air heated by the patient's body impinges on theindividual sensing elements 12, 14, and 16 thereby heating the narrowconduction loops and increasing the resistance of the entire multiplesensor system 10 as measured from connector pad 18 to connector pad 20when pads 19 and 21 are shorted together. Similarly, when the patientinhales, cooler air is drawn past individual sensing elements 12, 14,and 16 causing the measurable resistance from connector pad 18 toconnector pad 20 to decrease. Respiration is detected by theseresistance changes. The rate and amount of the resistance changeprovides data concerning the nature of the respiration.

If more detailed information is desired regarding nose versus mouthbreathing, connector pads 19 and 21 may be unshorted and separatemeasurements made from pads 18 and 19, as well as pads 20 and 21.

Bending and motion of the device does not change the overall resistancesignificantly because the interconnections of the active elements is ofvery low resistance elements. Optimal mechanical design minimizes motionartifacts from the individual sensing elements.

FIG. 1B is a plan view of an alternative embodiment of a multiple sensorsystem 210 employing conductive ink to fabricate the individual sensorsand the conducting paths. This embodiment uses a substrate 34, which maybe the same as that used for the embodiment of FIG. 1A, or in thealternative may be a clear mylar. The components of substrate 34 are aspreviously described.

For this embodiment, individual sensor elements 212, 214, and 216 arethermoresistive elements of a conductive ink which are silk screened onsubstrate 34. The conductive ink used for this purpose has a relativelyhigh resistance and preferably a high temperature coefficient ofresistance, such as Electrodag 423SS resistive carbon ink available fromAcheson Cholloids Co. of Chicago, Ill. Interconnecting conducting paths222, 224, 226, 228, and 229 are of a second type of conductive ink, suchas Electrodag 427SS conductive silver ink, which is silk screened intoposition during a subsequent process step. This second type ofconducting ink is selected to have a much lower resistance. Connectorpads 218, 219, 220, and 221, along with test connector pad 230, are silkscreened from the second type of conductive ink.

Operation of this embodiment is similar to the operation of theembodiment of FIG. 1A.

FIG. 2 is an electrical schematic diagram of multiple sensor system 10.All referenced components are as previously described. Individualsensing elements 12, 14, and 16 are shown as variable resistanceelements using the standard thermistor symbol. Conducting paths 22, 24,26 and 28 are shown as low resistance elements reflecting theirdistributed resistance. An equivalent schematic diagram (not shown)could be used to depict multiple sensor system 210.

FIG. 3 is a plan view of multiple sensor system 110, which uses analternative method of fabrication. Substrate 134 is a flexibleinsulator. It is preferably of Mylar or other suitable polymer, and maybe transparent or may be made of moisture resistant paper material.Substrate 134 is shaped similar to substrate 34 except that it has anextension of tab 138, for conduction paths 122 and 128, which terminatein connector assembly 142 and connector pins 144 and 146.

As with multiple sensor system 10, individual sensor elements 112 and114 are positioned for the nostrils of the patient, and individualsensor element 116 is placed to detect flow from the mouth. Electricalconduction paths 124 and 126 couple individual sensor elements 112, 114,and 116 in series.

Multiple sensor system 110 functions in a manner similar to multiplesensor system 10 (see also FIG. 1) except that it is somewhat easier tofabricate and can use a more flexible and less expensive substrate.

FIG. 4 is a plan view of multiple sensor system 110 as completelypackaged. Packaging is accomplished by covering substrate 134 withadhesive strip 150 in the manner described in more detail below.Adhesive strip 150 is attached to backing substrate 148 for storage andtransport. All other referenced elements are as previously described.

FIG. 5 shows the package of FIG. 4 as partially disassembled. Adhesivestrip 150 is configured as shown from a single piece of single sidedmedical adhesive tape. Substrate 134 is adhesively affixed to theadhesive side of main portion 152 as shown. Adhesive strip 150 is foldedalong line 156 such that minor portion 154 also is adhesively attachedto substrate 134. Adhesive strip 150 is formed to completely coversubstrate 134 except for individual sensing elements 112, 114, and 116.Tab 138 can be coated with a non-conducting high dielectric materialusing screening techniques, or tape 150 can be extended and folded overtab 138 to protect the conductors.

FIG. 6 is a side sectioned schematic view of the major components of thefully packaged multiple sensor system 110. The view is schematic in thatit is not drawn to scale for matters of illustration. All referencedcomponents are as previously described.

Backing substrate 148 is a single layer of flexible polymer. It is usedto protect the exposed surface of adhesive strip 150 during storage andtransport.

Main portion 152 of adhesive strip 150 has a flexible inner substrate160 of braided or woven polymer fibers. Adhesive layer 162 is depositedon the inner surface of substrate 160. Minor portion 154 of adhesivestrip 150 is, as explained above, preferably made as a single piece withmain portion 152.

FIG. 7 is a side view of the packaged multiple sensor system 110 withbacking substrate 148 removed. All referenced elements are as previouslydescribed.

FIG. 8 is a frontal view of patient 170 with multiple sensor system 110adhesively attached. The attachment is accomplished by removing majorportion 152 from backing substrate 148 and placing it over the upper lipof patient 170. Because substrate 134 is flexible, multiple sensorsystem 110 readily conforms to the contours of the upper lip of patient170.

As properly positioned, individual sensor elements 112 and 114 arelocated within the air streams of the nostrils of patient 170.Individual sensor element 116 is positioned over the air stream from themouth of patient 170.

FIG. 9 is a side view of patient 170 with a sectioned view of multiplesensor system 110 to show positioning of the individual sensingelements. It can be readily seen that individual sensing elements 112,114 (not shown), and 116 are inclined from the plane of substrate 134away from patient 170. Positioning the individual sensing elements inthis non-planar fashion places the individual sensing elements withinthe respective air stream and away from the skin of patient 170.

Tab 136 positions the system against the nasal septum of the nose sothat individual sensing elements 112 and 114 do not occlude thenostrils. Tab 136 can be made concave to better center the system underthe nose.

Having thus described the preferred embodiments of the presentinvention, those of skill in the art will readily appreciate that yetother embodiments may be utilized to practise the present inventionwithin the scope of the claims hereto attached.

I claim:
 1. A method of fabricating a medical sensor for determining theexistence of respiration, comprising:preparing an insulative flexiblesubstrate; constructing a temperature sensor by silk screening aconductive path having a first region and a second region onto saidsubstrate; wherein said first region comprises a first thin layer ofconductive ink with a first resistance and a temperature coefficient ofresistance, and said second region comprises a second thin layer ofconductive ink with a second resistance lower than said firstresistance, the temperature coefficient of resistance of said firstregion being relatively high, and wherein at least a portion of thefirst region forms a temperature sensing element; and forming at leastfirst and second electrical connectors at spaced points along saidconductive path for connecting the temperature sensor to an apparatusfor measuring a resistance change of the conductive path in response toa temperature change of the portion of the first region forming atemperature sensing element.